Initializing State Estimation for Aerial User Equipment (UES) Operating in a Wireless Network

1. A method for estimating movement of an aerial user equipment (UE) by a first radio access network (RAN) node serving the aerial UE in a cell of the RAN, the method comprising: determining initialization parameters for an interacting multiple-model (IMM) for movement of the aerial UE in the cell, wherein the determined initialization parameters include one or more of the following: a plurality of neighbor cells, in the RAN, in which positioning measurements should be performed for the aerial UE, and for at least one movement mode of the IMM, an initial state comprising a plurality of initial position estimates for the aerial UE; and determining a movement state for the aerial UE at a first time based on: the determined initialization parameters, and positioning measurements of the aerial UE that are performed in the cell and in at least a portion of the neighbor cells.

2. The method of claim 1, wherein determining the initialization parameters comprises selecting the plurality of neighbor cells in the RAN based on one or more of the following criteria: least distance from the center of the cell serving the aerial UE; antenna coverage in the direction of the center of the cell serving the aerial UE; and randomly from a number of suitable neighbor cells that is greater than the plurality.

3. The method of claim 1, further comprising: receiving, at each of one or more second times, positioning measurements for the aerial UE performed in at least a portion of the neighbor cells; and selecting a subset of the neighbor cells based on one or more of the following: likelihood that each neighbor cell will report positioning measurements for the aerial UE; and quality of received positioning measurements performed in each neighbor cell.

4. The method of claim 3, further comprising determining further initialization parameters, for the IMM, that include the selected subset of the plurality of neighbor cells that were included in the initialization parameters.

5. The method of claim 1, wherein the positioning measurements include measurements of one or more of the following: range or distance between the UE and an antenna for the cell; range or distance between the UE and respective antennas for the neighbor cells; and range rate or Doppler shift between the UE and respective antennas for the cell and the neighbor cells.

6. The method of claim 5, wherein: the plurality of neighbor cells include at least three neighbor cells; and the positioning measurements only include range rate or Doppler shift between the UE and the respective antennas for the cell and the neighbor cells.

7. The method of claim 1, wherein the IMM model includes: a first model, including an almost-constant velocity model with a Doppler shift bias state, a second model, including at least one maneuver model with a Doppler shift bias state, and estimated probabilities associated with the first and second models.

8. The method of claim 7, wherein: the IMM model also includes a Hidden Markov Model (HMM) comprising respective transition probabilities of the aerial UE between any of the first and second models during successive updates of the movement state; and each transition probability is dependent on the duration between successive updates of the movement state.

9. The method of claim 7, wherein determining the movement state for the aerial UE at the first time comprises: determining first and second movement states for the aerial UE based on the respective first and second models; and combining the first and second movement states according to estimated probabilities associated with the first and second models.

10. The method of claim 8, wherein the first and second movement states are determined using respective extended Kalman filters (EKFs).

11. The method of claim 8, wherein: the second model includes a plurality of maneuver models associated with a respective plurality of initial position estimates and a respective plurality of estimated probabilities; and determining the movement state for the aerial UE at the first time comprises determining states for the respective maneuver models at the first time based on the positioning measurements and the respective initial position estimates.

12. The method of claim 11, further comprising: determining movement states for the aerial UE at a plurality of second times after the first time, including updated states for the first model and for the respective maneuver models; subsequently determining respective sums of the updated estimated probability associated with the first model with the respective updated estimated probabilities associated with the respective maneuver models; and selecting one of the maneuver models for which the determined sum is within a threshold difference from unity.

13. The method of claim 12, further comprising determining a movement state for the aerial UE at a third time after the second times, including updated states only for the first model and the selected maneuver model.

14. The method of claim 12, wherein determining the initial state for the IMM comprises selecting the plurality of initial position estimates for the plurality of maneuver models based on one or more of the following criteria: the center of the cell serving the aerial UE; randomly from a coordinate space of the cell serving the aerial UE; a deterministic grid of points in the coordinate space of the cell serving the aerial UE; and a deterministic grid of points near boundaries of the cell serving the aerial UE.

15. The method of claim 14, wherein the plurality of initial position estimates include: a first number of points selected from the deterministic grid of points near boundaries of the cell serving the aerial UE, and a second number of points selected according to a different one of the criteria.

16. The method of claim 14, wherein the coordinate space of the cell serving the UE is bounded in altitude by a maximum altitude of the aerial UE.

17. The method of claim 12, wherein: the plurality of maneuver models are also associated with a respective plurality of initial covariance matrices; and determining the movement state for the aerial UE at the first time comprises determining initial covariance matrices for the respective maneuver models at the first time based on one or more of the following: radius of the cell serving the aerial UE, maximum altitude of the aerial UE, maximum velocity of the aerial UE, and maximum acceleration of the aerial UE.

18. The method of claim 1, further comprising: sending respective state estimation initialization messages to one or more neighbor RAN nodes serving the plurality of neighbor cells; receiving respective state estimation reports from the one or more neighbor RAN nodes; and receiving, from the one or more neighbor RAN nodes, respective measurement reports including the positioning measurements for the aerial UE performed in at least a portion of the neighbor cells.

19. A method for a second radio access network (RAN) node configured to serve one or more neighbor cells of a cell serving an aerial user equipment (UE) in the RAN, the method comprising: receiving, from a first RAN node serving the cell, a state estimation initialization message indicating that positioning measurements should be made for the aerial UE in the one or more neighbor cells; and sending, to the first RAN node, a state estimation report including one or more of the following for each of the one or more neighbor cells: identifier of the neighbor cell, type of antenna used for the neighbor cell, geographic location of the antenna for the neighbor cell, direction or orientation of the antenna for the neighbor cell, and downlink transmission power used in the neighbor cell.

20. The method of claim 19, further comprising: performing the indicated positioning measurements for the aerial UE in the one or more neighbor cells; and sending, to the first RAN node, a measurement report including the positioning measurements for the aerial UE in the one or more neighbor cells.

21. A first radio access network (RAN) node configured to estimate movement of an aerial user equipment (UE) in a cell served by the first RAN node, the first RAN node comprising: communication interface circuitry configured to communicate with one or more neighbor RAN nodes; and processing circuitry operably coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the method of claim 1.

22. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a first radio access network (RAN) node configured to estimate movement of an aerial user equipment (UE) in a cell served by the first RAN node, configure the first RAN node to perform operations corresponding to the method of claim 1.

23. A second radio access network (RAN) node configured to serve one or more neighbor cells of a cell serving an aerial user equipment (UE) in the RAN, the second RAN node comprising: communication interface circuitry configured to communicate with a first RAN node serving the cell; and processing circuitry operably coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the method of claim 19.

24. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a second radio access network (RAN) node configured to serve one or more neighbor cells of a cell serving an aerial user equipment (UE), configure the second RAN node to perform operations corresponding to the method of claim 19.